KIEV, Ukraine -- Fierce fighting raged in eastern Ukraine on Thursday in what appeared to be a last-gasp attempt by government troops to snatch back territory from pro-Russian separatists before the arrival of a Russian aid convoy overseen by the Red Cross.

Trucks loaded with water, generators and sleeping bags for desperate civilians in the besieged city of Luhansk began moving through Ukrainian customs after being held up at the border for a week, in part because of safety concerns and Ukrainian fears that the convoy's arrival could halt the military's advance.

The trucks in the 200-vehicle convoy were expected to cross into Ukraine on Friday morning on their way to Luhansk, a city with a war-reduced population of a quarter-million people, 20 kilometres (12 miles) from the Russian border.

At Russia's urging, U.N. Secretary-General Ban Ki-moon called for a cease-fire during the humanitarian mission.

The Red Cross has said it needs assurances of safe passage from all sides to bring in the supplies and set up distribution points, so even without a formal cease-fire, Ukrainian government forces could be severely constrained in their movements once the trucks begin moving.

Ukrainian troops have made significant advances into rebel-held territory this week in a conflict that has claimed more than 2,000 lives and forced over 340,000 people to flee their homes. Ukraine celebrates Independence Day on Sunday, and there are widespread suspicions the government is anxious for a breakthrough by then.

Looking for a diplomatic solution to the crisis, Ukrainian President Petro Poroshenko will meet on Saturday with German Chancellor Angela Merkel, who has acted as a mediator, and will sit down with Russian President Vladimir Putin in Minsk, Belarus, early next week.

"We are going to Minsk to talk about peace," Poroshenko said in a statement. "The whole world is tired of war."

Poroshenko stopped short of saying whether he still insists on the rebels' unconditional surrender.

Ukraine has accused Russia of arming and supporting the separatists since the fighting began in mid-April, a charge Russia denies.

Meanwhile, five troops were killed and two civilians died over a 24-hour period in rebel-held areas, authorities said. That followed over 50 deaths on Wednesday.

Troops fought separatists in and around Ilovaysk near the rebel-held city of Donetsk, and at least two people were killed and an unspecified number wounded in an artillery strike on a Donetsk suburb, authorities said.

Once home to 1 million, Donetsk, the largest city still held by the rebels, has seen one-third of its population flee since the spring.

Heavy fighting was also reported in Luhansk on Thursday, a day after the government said it had retaken much of the rebel stronghold. The city has been under siege for 19 days, lacking such basics as running water and electricity.

"People hardly leave their homes for fear of being caught in the middle of ongoing fighting, with intermittent shelling into residential areas placing civilians at risk," the Red Cross said.

Laura Mills and Lynn Berry in Moscow and Frank Jordans in Berlin contributed to this report.

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About 60 trucks forming part of a Russian aid convoy are parked in a field about 7 kilometres from a border control point with Ukraine in the Russian town of Donetsk, Rostov-on-Don region, Russia, Thursday, Aug. 21, 2014. (AP / Pavel Golovkin)